1. Field of the Invention
The invention relates to a process for the preparation of a high-purity, thermally stable catalyst carrier based on an aluminosilicate with 0.5 to 50% by weight of SiO.sub.2 by mixing an aluminum compound with a silicic acid compound in an aqueous medium and subsequent drying or calcining of the product obtained.
2. Description of the Prior Art
Processes for the preparation of aluminosilicate are based either on the joint precipitation of silicic acid compounds and aluminum compounds in an aqueous medium, or on impregnation processes.
Thus, e.g. EP-A1-0 238,760 describes a process in which a --Al.sub.2 O.sub.3 carrier is impregnated with a colloidal SiO.sub.2 solution in water and is subsequently dried for a long time at temperatures above 120.degree. C. In another process according to British patent 2,129,701 or European patent A3-0 190,883 alumina carriers are either contacted with a silane or with a water-dispersed polyorganosiloxane and subsequently calcined.
The aluminosilicates obtained according to this process are either unsatisfactory with regards to their high purity, particularly with regards to the presence of alkali metal and alkaline earth elements, or take a long time or are complicated to prepare and in particular do not make it possible to prepare high purity aluminosilicates, whose composition can be adjusted at random with regards to the SiO.sub.2 content. The thermal stability of these catalyst carriers is also inadequate in many cases.
In the field of heterogeneous catalysis, high-purity catalyst carriers are required, whose sodium content is below 50 ppm Na.sub.2 O and in which the sum of Al.sub.2 O.sub.3 and SiO.sub.2 is at least 99.95% by weight. According to the latest findings much greater significance is attached to the carrier substances for the active components, because the carrier not only permits a fine distribution of the active components over the surface and the ideal mass transport by means of specifically set pore structures, but, as a function of the pore size, SiO.sub.2 content and acidity has synergistic effects with the catalytically active substances. This is particularly important with aluminosilicates and in the present case carrier materials with a greater tendency to amorphous structures or aluminum oxide crystal structures are involved rather than zeolites. With a view to the uses of catalyst carriers, such as desulphurization, dentrificaton, oxiation, hydrocracking, mild hydrocracking, exhaust gas detoxification and the various isomerization reactions, it is necessary to correspondingly adjust the aluminosilicates with regards to the acidity of and the SiO.sub.2 content.